Thermally switched optical filter incorporating a guest-host architecture

ABSTRACT

Thermochromic filters are constructed using absorptive, reflective, or fluorescent dyes, molecules, polymers, particles, rods, or other orientation-dependent colorants that have their orientation, order, or director influenced by carrier materials, which are themselves influenced by temperature. These order-influencing carrier materials include thermotropic liquid crystals, which provide orientation to dyes and polymers in a Guest-Host system in the liquid-crystalline state at lower temperatures, but do not provide such order in the isotropic state at higher temperatures. The varying degree to which the absorptive, reflective, or fluorescent particles interact with light in the two states can be exploited to make many varieties of thermochromic filters. Thermochromic filters can control the flow of light and radiant heat through selective reflection, transmission, absorption, and/or re-emission. The filters have particular application in passive or active light-regulating and temperature-regulating films, materials, and devices, and particularly as construction materials and building and vehicle surfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/758,573 filed 12 Apr. 2010 entitled “Thermally switched opticalfilter incorporating a guest-host architecture,” now U.S. Pat. No.8,284,336, which claims the benefit of priority pursuant to 35 U.S.C.§119(e) to the following: U.S. provisional patent application No.61/168,513 entitled “Large throw thermoreflective and thermoabsorptivefilters” filed 10 Apr. 2009; U.S. provisional patent application No.61/262,024 entitled “Thermally switched optical filter” filed 17 Nov.2009; U.S. provisional patent application No. 61/296,127 entitled“Thermally switched optical filter incorporating a guest-hostarchitecture” filed 19 Jan. 2010; and U.S. provisional patentapplication No. 61/299,505 entitled “Thermally switched optical filterincorporating a guest-host architecture” filed 29 Jan. 2010. Thedisclosures of each of these applications are hereby incorporated hereinby reference in their entirety.

In addition, this application is related to U.S. patent application Ser.No. 12/172,156 entitled “Thermally switched reflective optical shutter”filed 11 Jul. 2008, now U.S. Pat. No. 7,755,829; U.S. patent applicationSer. No. 12/340,552 entitled “Thermally switched absorptive windowshutter” filed 19 Dec. 2008; and U.S. patent application Ser. No.12/019,602 entitled “Thermally switched optical downconverting filter”filed 24 Jan. 2008, now U.S. Pat. No. 7,768,693; U.S. patent applicationSer. No. 12/234,383 entitled “Low emissivity window films and coatingsincorporating nanoscale wire grids” filed 19 Sep. 2008; U.S. patentapplication Ser. No. 12/429,092 entitled “Glare management of reflectiveand thermo reflective surfaces” filed 23 Apr. 2009, U.S. patentapplication Ser. No. 12/497,365 entitled “Insulating glass unit asshipping container” filed 2 Jul. 2009; U.S. patent application Ser. No.12/545,051 entitled “Methods for fabricating thermochromic filters”filed 20 Aug. 2009; and U.S. patent application Ser. No. 12/488,515entitled “Optical metapolarizer device” filed 19 Jun. 2009; and thedisclosures of each are hereby incorporated herein by reference in theirentirety.

BACKGROUND

1. Field of Technology

This technology relates to a device for controlling the flow of lightand radiant heat through selective absorption or reflection of light.The technology has particular, but not exclusive, application in passiveor active light-regulating and temperature-regulating films, materials,and devices, especially as a construction material.

2. Description of the Related Art

Switchable mirrors exist which are based on reversible metal hydride andmetal lithide chemistry described, for example, in U.S. Pat. No.7,042,615 to Richardson. These switchable mirrors, which are chemicallyrelated to rechargeable batteries, may rely on the physical migration ofions across a barrier under the influence of an electric field and,therefore, have limited switching speeds and cycle lifetimes. Inaddition, electrically operated “light valves” that combine liquidcrystals with one or more reflective polarizers are described, forexample, in U.S. Pat. No. 6,486,997 to Bruzzone et al. In these devices,a liquid crystal typically serves as an electrotropic depolarizer, i.e.,a means of variably altering or rotating the polarity of the light thatpasses through it, under the influence of an electric field. Some ofthese devices can be thought of as switchable mirrors, although they arerarely described that way, since their primary application is in videodisplays, video projectors, and advanced optics.

Switchable electric light valves that do not require polarizers, but arediffusive forward scatterers or diffusive reflectors, also exist. Thisis because liquid crystals themselves may act as reflectors (includingbut not limited to distributed Bragg reflectors or DBRs) with differentreflection bands in these applications, with a reflective, diffusive, orforward-scattering mode, and a more transmissive mode. These include thepolymer-dispersed liquid crystal (PDLC) display, the cholesteric liquidcrystal display (Ch-LCD), the Heilmeier display, and the Guest-Hostdisplay. The PDLC is an electrochromic device where the index ofrefraction of liquid crystal droplets embedded in another material ischanged electrically, resulting in more scattering of the light in onemode than another. The Ch-LCD has two stable states, the reflectiveplanar and focal conic texture. The reflective planar structure reflectslight if the Bragg reflection condition is met and thus acts as a Braggreflector for one circular polarization of light, while the reflectivefocal conic transmits more of the light.

An optical structure called a Guest-Host display commonly utilizes dyesdispersed in a liquid crystal, which absorb more light when in oneorientation than in another. The orientation of the dyes is dependent onthe orientation of the liquid crystal, which is determined using anelectric field created by a voltage, typically applied via transparentconducting layers such as indium tin oxide. Such devices may alsoutilize one or more polarizers. There are positive and negative dichroic(pleochroic and negative dichroic) dyes, among others, whichrespectively absorb light along different axes of the molecule.

Polymer-stabilized liquid crystals are created when prepolymers andliquid crystals are mixed and the prepolymer is polymerized, to amongother things establish or reinforce the orientation of the liquidcrystals. Liquid crystal mixed with prepolymers which are cured invarious ways and concentrations has been described in the literature,among other terms, as polymer-stabilized, polymer-networked,polymer-enhanced, and polymer-dispersed, among many other terms. Thistechnology is well described in the prior art as, for example, in U.S.Pat. No. 7,355,668 to Satyendra et al., which discloses polymer-enhancedliquid crystal devices, specifically electrically operated displaydevices, built with rigid or flexible substrates that include polymer“columns” formed between substrate films through the phase separation ofa prepolymer (e.g., Norland NOA77 or 78 optical adhesive) and a liquidcrystal (e.g., Merck E7, E48, or E31), under the influence oftemperature variations. The prepolymer and liquid crystal are mixedabove the clearing point temperature of the LC, and are then cooledbelow the clearing point in order to separate, polymerize, and solidifythe polymer network within the liquid crystal material.

More recently, in U.S. patent application Ser. No. 12/172,156 to Powerset al., thermotropic liquid crystal shutters have been described,wherein a thermotropic liquid crystal is placed between two crossedpolarizers, such that in one temperature state the liquid crystal formsa twisted nematic waveblock that rotates the polarity of incoming light,allowing the light transmission, absorption, and reflection propertiesof a single polarizer, while in another temperature state the liquidcrystal is in an isotropic state, such that it does not affect thepolarization state of incoming light. The device has the opticalproperties of two crossed polarizers, allowing much lower transmissionand much higher absorption or reflection of incident light. Theinformation included in this Background section of the specification,including any references cited herein and any description or discussionthereof, is included for technical reference purposes only and is not tobe regarded as subject matter by which the scope of the invention is tobe bound.

SUMMARY

The technology disclosed herein is directed to the temperature-basedcontrol over transmissivity, reflectivity, or absorptivity with regardto radiant energy (e.g., visible, UV, and infrared light), including upto the entire range of the solar spectrum, for the purpose of regulatingthe flow of heat into a structure (e.g., a window, building, or vehicle)based on external weather conditions, internal temperature, or anycombination of the two, responding over a range of temperatures thatmake it useful for these purposes. This technology is a device havingtemperature-responsive transmission, absorption, or reflection of lightenergy, effected by temperature-induced changes in, among other things,the structure, phase, or order of a thermotropic carrier material (e.g.,a thermotropic liquid crystal), which provides temperature-dependentorder (or induces temperature-dependent order) to one or more includedcomponents that interact with light (e.g., reflective or absorptivedyes, polymers, or inorganic markers), which, for purposes of thisdocument, shall be referred to as “orientation-dependent colorants”(ODCs). Similar to usage with liquid crystal devices generally, theparticular local spatial orientation characteristics of the thermotropiccarrier material at a given temperature state shall be known as a“director.” It should be understood that a particular thermotropiccarrier material (e.g., a thermotropic liquid crystal), when used as acomponent of an embodiment described herein, may exhibit two or morediscrete directors, or an analog range of directors, at differenttemperature states.

For example, at one temperature the thermotropic carrier material mayinduce significant order in one or more included ODCs (potentiallyincluding absorptive, reflective, or fluorescent molecules, dyes,particles, rods, polymer chains, or any combination thereof) suspendedor dissolved within the thermotropic carrier material, while at a secondtemperature may provide little or no preferred director for these ODCs.If the director associated with the first temperature is chosen suchthat the included components interact less with light at the firsttemperature than the second temperature, the optical properties such astransmission, absorption, and fluorescence will be different at the twotemperatures. The efficiency of absorption, reflection, or transmissioncan be varied through the selection of the included ODC materials, ascan the frequency-dependent efficiencies. The choice of ODC materialsmay be used to affect percentages and wavelength ranges of reflection,absorption, and transmission above and below a threshold temperature, orover a selected range of temperatures, that are desirable foraesthetics, energy management, or other reasons.

Additionally, if the included ODC materials are reflective, the devicemay be diffusively reflective due to the distribution of orientations ofthe included materials. This technology has particular, but notexclusive, application as a glare reduction method for buildingsurfaces. The efficiency, spatial distribution, bandwidth, and centerwavelength of reflection can be varied as the orientation of the ODCchanges under the influence of the thermotropic carrier material.Examples of reflective ODC materials include flakes, wires, rods,particles, or filaments. These may be composed of metals; of polymers orinorganic ceramic-type materials that are white or otherwise reflectivein color; of polymers or inorganic ceramic-type materials that aretransparent but which have refractive indices indexes significantlymismatched to that of the thermotropic carrier material; of polymerchains (e.g., polyacetylene) that have inherent reflectivities due to anelectrically conductive nature; or of related materials or anycombination thereof.

This technology may also be employed as a part of a device operatingsimilarly in function to a temperature-responsive optical depolarizer,(for example, a thermotropic liquid crystal) operating with one or morepolarizing filters to regulate the passage of light energy. The orderprovided or induced in the included materials can be polarizing (intransmission or reflection) at one temperature, and less polarizing oreven non-polarizing in another. The incident energies passing throughthis device will therefore depend on the reflection and absorptionefficiencies of both the ODCs and of the polarizers used. For example,when the ODC is induced at one temperature to be a functionallyefficient polarizer, and paired with a second efficient polarizer whichtransmits light of this same polarization, then half of the incidentradiant energy passes through the device. However, if a temperaturechange reduces the order of the ODC such that the ODC will blocktransmission of light of both polarizations, then the amount of lighttransmitted through the device may therefore change as well. Lowerefficiency polarizers, or ODCs and polarizers with frequency-dependentefficiencies, may be selected to affect percentages of reflection,absorption, and transmission above and below a threshold temperature orover a selected range of temperatures that are desirable for aesthetics,energy management, or other reasons. This effect can be such that thedevice is less transmissive in either its hot or cold state, or expandedsuch that the transmissivity of the device is higher in the transparentstate. Angle-dependent optical effects may also exist.

The thermotropic carrier material may also induce different amounts oforder in one or more included ODCs (whether absorptive, reflective, orfluorescent molecules, dyes, particles, rods, polymers, or anycombination thereof) suspended or dissolved within the carrier materialat different temperatures. For example, the thermotropic carriermaterial, and any associated alignment layers or structures, may beselected such that the amount of order provided may decrease withincreasing temperatures. If the director associated with the ODC ischosen such that the included components interact more with light as thetemperature increases, the optical properties such as transmission,absorption, and fluorescence will therefore vary as the temperatureincreases. Alternatively, among other possibilities, the director may bechosen such that the included ODCs interact more with light at lowertemperatures than at higher temperatures, or the order provided mayincrease with increasing temperature. Such devices are described, forexample, in “Dichroic Dyes for Liquid Crystal Displays” by Alexander V.Ivashenko and “Liquid Crystals” (Second Edition) by S. Chandrasekhar,incorporated herein by reference. These effects may also be combinedwith other effects, such as those previously described, where order ispresent at one temperature and not at a second, or where the orderchanges precipitously at a given temperature or across a temperaturerange, or with other effects such as having different orders for a giventemperature based on the temperature history (e.g., supercooling andhysteresis effects). The efficiency of absorption, reflection, ortransmission response for different directors may be varied through theselection of ODC materials, as can the wavelength-dependentefficiencies. The choice of materials may be used to affect percentagesand wavelengths of reflection, absorption, and transmission above andbelow a threshold temperature, or over a selected range of temperatures,that are desirable for aesthetics, energy management, or other reasons.

This technology may employ both specular and diffusive optical effectsas described above, to create windows or window filters that exhibitboth transparent and opaque privacy-type modes, and prevent theconcentration of reflected solar energy in UV, visible, or IR bands indifferent ways. This technology may also be used to absorb, reflect ortransmit, diffusively or specularly, various polarizations andwavelength ranges of light in different ways at different temperatures,to achieve particular aesthetic, privacy, glare, or solar heat gainproperties.

Other features, details, utilities, and advantages of the presentinvention may be apparent from the following more particular writtendescription of various embodiments of the invention as furtherillustrated in the accompanying drawings and defined in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary implementation of athermochromic filter having ODC materials suspended or dissolved in athermotropic carrier material (e.g., a thermotropic liquid crystalhaving molecules aligned perpendicular to the substrate) that providesor induces order for the ODC materials at a lower temperature and doesnot at a higher temperature.

FIG. 2 is a schematic view of an exemplary implementation of athermochromic filter used in combination with a polarizer. Thethermochromic filter has ODC materials suspended or dissolved in athermotropic carrier material (e.g., a thermotropic liquid crystalhaving molecules are aligned parallel to the substrate) that provides orinduces order for the ODC materials at a lower temperature and does notat a higher temperature.

FIG. 3 is a schematic view of another exemplary implentation of athermochromic filter having ODC materials suspended or dissolved in athermotropic carrier material e.g., a vertically-aligned thermotropicliquid crystal) that provides or induces more order in the ODC materialsat a lower temperature than it provides at a higher temperature.

FIG. 4 is a schematic view of a further exemplary implementation of athermochromic filter having ODC materials suspended or dissolved in athermotropic carrier material (e.g., a vertically aligned thermotropicliquid crystal) where the directional polarizing properties of one ormore thermotropic polarizer layers are used to vary the transmissionproperties (including polarizing effects) of the filter based on thedirection of the light being transmitted.

DETAILED DESCRIPTION

For the purposes of this specification, the term “thermoreflective”shall refer to any object, device, or material having a reflectivitythat varies as a function of temperature. Similarly, “thermoabsorptive”and “thermoflourescent” shall refer to any objects, devices, ormaterials having an absoptivity or fluorescence, respectively, thatvaries as a function of temperature. Since light transmission is afunction of reflection, absorption, and re-radiation of light, any ofthese objects, devices, or materials may also be properly described bythe more generic term, “thermochromic”.

FIG. 1 is a schematic, cross-section view of an exemplary form of athermochromic filter device 100. The filter device 100 may be composedof included “orientation dependent colorant” or ODC materials 101 insidea transmissive, thermotropic, order-providing carrier material 102. At alower temperature, assuming that the ODC molecules interact morestrongly with incoming light perpendicular to their long axis, asignificant percentage of the incoming light passes through theorder-providing carrier material 102 as well as the included ODCmaterials 101 due to their ordered orientation with respect to theincoming light. As with a shutter or venetian blind in the “open” state,the ODC materials are essentially parallel to the incoming light andthus do not substantially absorb or reflect it. At a higher temperature,more of the incoming light is blocked due to the unordered orientationof the included ODC materials, a large fraction of which are no longerparallel to the incoming light and are therefore capable of absorbing,reflecting, or otherwise interacting with it. It is notable that whenthe included ODC materials are in the ordered state, the filter device100 is capable of polarizing light that enters the filter device 100from directions other than the one indicated in the figure, and thus maybe considered a “thermotropic polarizer” for some purposes.

Additional polarizers or other optical elements may also be added toproduce different optical effects without affecting the essential naturethermochromic filter device 100.

The thermotropic carrier material 102 may take a variety of differentforms for use within the thermochromic filter device 100. Many materialsthat are transparent to at least some wavelengths of light alsoexperience changes of the amount of order of their molecules (or changesin their director or directors) with changes in temperature. Inparticular, many thermotropic liquid crystals are optically transparentwith high (almost crystalline) order in the liquid crystalline state(i.e., nematic state), while being optically transparent with low order(e.g., a randomly or semi-randomly oriented state) in the isotropicstate.

The director of liquid crystal molecules in a liquid crystal state (suchas the nematic or smectic states) near a surface can be influencedthrough the use of alignment layers. Both vertical (homeotropic) andparallel (homogeneous) alignments are common, where the director of theliquid has respectively, a director normal or parallel to the surface.The director can be affected by the surface energy and chemistry of thesurface. In general, high surface energy promotes parallel alignment andlow surface energy promotes vertical alignment. In the prior art,polydimethylsiloxanes, for example, are commonly used to promotevertical alignment and rubbed polyimides, for example, are used topromote parallel alignments. Methods for promoting various alignmentsand pre-tilt angles, their intermediaries, hybrids, combinations, andthe resulting useful structures when liquid crystal molecules are placednear one, two, or more surfaces are generally known, have been welldescribed in the prior art, and will be familiar to a person of ordinaryskill in the art. More complex orientation states also exist and havealso been described. For example, in the liquid crystal “blue phase,”the director of the liquid crystal molecule rotates in a helical fashionabout any axis perpendicular to a line.

If the thermotropic carrier material is a liquid crystal (LC) material,it may be required to meet environmental tolerance specifications thatare consistent with the environment in which the device is to be used.For example, in an exemplary thermochromic window application the LC mayrequire a clearing point between 20° C. and 35° C., a freezing pointbelow −40° C., a boiling point above 90° C., and enough UV resistance tosurvive 30 years of daily exposure to sunlight (possibly attenuated byglass, polarizers, UV-blocking adhesives, and other materials inherentin the thermochromic window structure). Other requirements may alsoexist, such as a birefringence sufficient to produce the desiredretardation across a particular cell gap. In particular it may bedesirable for the device to have a small cell gap in order to minimizethe amount of liquid crystal required. This would in turn imply aminimum birefringence for the LC mixture, in order to achieve thedesired optical effects.

In general for LC mixtures, properties such as birefringence andclearing point are close to the weighted average of the individualcomponents, whereas properties like UV resistance or chemical resistancemay be limited by, or more strongly dependent on, the resistance of theleast resistant component. Additionally, properties such as freezingpoint depend on the interactions of individual molecules, which becomeless favorable for crystallization as the molecules become moredissimilar from one another. Thus, when two LC components are mixedtogether, the resulting mixture may exhibit a freezing pointsignificantly lower than either component by itself. Also, while thesolubility of different LC components differs significantly depending ontheir molecular structure, the solubility may be improved when differentcomponents are present in the mixture, i.e., the solubility of two mixedcomponents in a third component may be greater than the solubility ofeither component separately.

For example, although 7CB liquid crystal has a freezing point ofapproximately 30° C. and a clearing point of approximately 41° C., whenmixed in equal proportions with 5CB liquid crystal, which has a freezingpoint of approximately 23° C. and clearing point of approximately 34°C., the LC mixture yielded has a clearing point of approximately 37° C.and a freezing point well below −70° C. However, this mixture may be nomore UV-stable than either of its components, and the chemicalsusceptibilities of both components still exist in the mixture, as bothmolecules are capable of acting as organic solvents, especially at hightemperature, and may thus attack certain organic substrate materials.

Mixtures of assorted LC components, which are combined to produceparticular thermal, physical, chemical, and optical properties(including “eutectic” mixtures), are generally known. Perhaps the bestknown commercial LC mixture is E7, which is commonly used in videodisplays and is a mixture of 5 different LC components. The dominantcomponent is 5CB (which has a low clearing point, good solubility, andsmall birefringence), but the mixture also contains significantquantities of 7CB, 8OCB, 5OCB, and 5CT (which has a high clearing point,poor solubility, and large birefringence). The mixture is designed tohave a broad nematic range, a high clearing point, and a low freezingpoint, and the high solubility of the 5CB helps overcome the lowsolubility of the 5CT. The principles and design rules of LC mixturessuch as these have been well described in the art.

In the prior art, dye molecules have sometimes been included in liquidcrystals in electrochromic devices as described, for example, in“Dichroic Dyes for Liquid Crystal Displays” by Alexander V. Ivashchenko.Such systems are often called Guest-Host systems and the devices calleddichroic devices. With proper selection of guest components (i.e., ODCs)and host components (i.e., electrotropic carrier materials), the dyemolecules assume (approximately) the director of the liquid crystalmolecule. Absorption and other related optical effects often occur alongan angle “near” the director of the ODC molecule, and can have a slightdifference (e.g., 5-10 degrees) between the director and maximumabsorption angle. There are positive (pleochroic) and negative dichroicdyes which respectively absorb light along different axes of themolecule. Therefore, some embodiments disclosed herein may be understoodas resembling an electrochromic Guest-Host system, except that thecarrier material has been designed such that it is thermotropic (asdescribed, for example, in U.S. patent application Ser. No. 12/172,156to Powers et al. entitled “Thermally switched reflective opticalshutter”), rather than electrotropic.

The orientation-dependent colorant (ODC) materials may also take anumber of forms. For example, pleochroic dye systems generally havehigher dichroic ratios and order parameters than negative dichroic dyesystems. Embodiments may be constructed that utilize either positive ornegative dichroic dyes, or a combination thereof, to affect differenttransmission properties across temperature ranges (e.g., shifting thecolor balance or hue). Performance of the dyes and system is affected byultraviolet light (UV) stability, solubility, and order parameter of thedye(s) within the system. Performance of the system is also affected byliquid crystal host parameters, viscosity, order parameter, temperaturerange of physical states, stability, and birefringence. Note thatGuest-Host systems for liquid crystals and dichroic dyes are often suchthat multiple dyes of one class are better at solvating, i.e., a mixtureof similar dyes may have a greater total concentration than would bepossible for any of the component dyes. Chemical “scaffolding” of dyescan also increase their solubility (e.g., attaching a liquid crystalmolecule chemically to the dye molecule).

These various properties can be used to design a device withdesirab\transmission properties. For example, if a particular dye hasotherwise desirable properties (e.g., high UV stability) but lowsolubility in the desired Host, the thickness of the Guest-Host systemcan be increased to increase the attenuation of light transmitted. Itshould also be understood that many dyes that are unsuitable forelectrochromic Guest-Host devices (e.g., cloth dyes) may be suitable forthermotropic devices because device operation is not contingent onelectric fields.

Chiral (dopant) molecules may also be added to Guest-Host systems tochange or improve the absorption or reflection of the guest(s). Forexample, a nematic liquid crystal system with multiple twists can beconstructed using such molecules in order to affect contrast ratio orother optical properties. Optically active molecules can also be used asguests in Guest-Host systems, and can be used to construct systems thatinteract (e.g., reflectively) with circular polarizations of light.

Semiconducting materials may also be used as guests to provide infraredabsorbing and reflecting Guest-Host systems.

Side-chain liquid crystals, polymer nematic liquid crystals, and nematicside-chain polymers, and other such Host systems may have slowerelectrochromic response times (or have no electrochromic response) whenused in electrochromic Guest-Host devices, but they may be particularlysuitable for thermotropic systems. Dye copolymers with liquid crystalmay be employed to improve effective solubility. Crystalline polymerliquid crystal with embedded or copolymer dyes may be employed toprovide a transition of order without a nematic or other such state.Such a device would not function electrochromically, but may be actuatedby a thermotropic carrier. Doped polyacetylene copolymers and/orside-chains with liquid crystal are also alternative embodiments ofsystems disclosed herein.

The order (or order parameter) of the Host system generally varies withtemperature (as described, for example, in “Liquid Crystals SecondEdition” by S. Chandrasekar) and the order (or order parameter) of theGuest or ODC varies with it. In general, for classes of liquid crystalHost chemistries or mixtures, as the clearing point increases, so doesthe order parameter of a particular Guest. Also, in general, as theclearing point of the resulting system is approached, the orderparameter drops. These variations in order (or order parameter) can becontinuous or discrete, or both, depending on the system and temperaturerange. For example, in Guest-Host nematic liquid crystal systems, theorder parameter of the host materials may be reduced by increases intemperature until the clearing point, where the liquid crystal thenbecomes isotropic, and then the order of both the Guest and Host may beeffectively eliminated.

It should be understood that the director of the order in such systemscan be determined using appropriate alignment materials and techniques.Further, the amount of order (order parameter) for a given Guestmaterial (i.e., the included ODC material) is a function of the Hostmaterial chosen as well as the temperature, and that through skillfulmaterials selection and system design, it is possible to achieve manydifferent relationships of temperature vs. order. One desirable propertyin a temperature relation is to have the order parameter of the Guestvary monotonically with temperature over the temperature design range ofthe device. Another desirable property is to incorporate hysteresis intothe temperature relation. For example, in a nematic, thermotropic liquidcrystal Guest-Host device utilizing the transition from nematic toisotropic states, it may be desirable for aesthetic reasons to have the“transition” temperature be several degrees higher when the device istransitioning from nematic to isotropic than when transitioning fromisotropic to nematic, as this will reduce the probability that thedevice will rapidly change transmission characteristics back and forthwhen near the transition temperature.

Polyacetylene is one polymer which can be modified chemically to becomehighly electrically conductive. This and other highly conductivepolymers can strongly interact with light reflectively, as in awire-grid polarizer, and the interaction can be dependent on theorientation of the molecule. Conductive polymers can also interact withlight absorptively, with the interaction dependent on the orientation ofthe molecule as well. Both polymers and dye molecules can be integratedinto polymer stabilized twisted nematic (PSTN) structures, as well asother polymer/liquid crystal systems. By choosing the order parameter ofthe doped polyacetylene properly, it will be possible to select theratio of forward to backward scattering of devices using conductivepolyacetylene, as well as made with other similar ODC Guests.Polyacetylene molecules can also have chemical “scaffolding” moleculesattached to them to increase their solubility.

Polyacetylene polymer can be manufactured into a reflective polarizer byusing it as the Guest with polymer liquid crystal as the Host, and thencooling the system until the polymers are fixed in place. Polyacetylenecan also be manufactured into reflective polarizers in processes likethose used to manufacture PVA-iodine polarizers.

The human eye responds to the relative amounts of several ranges ofvisible light. Thus many different spectral distributions may appearidentical to the human eye. Metamerism is the matching of apparent colorof objects with different spectral power distributions, and colors thatmatch this way are called metamers. The absorption, transmission,fluorescence, and reflection of light by molecules (such as dyemolecules) has a spectral (frequency) component to it. By properlyselecting components (e.g., combinations of dyes), it is possible toselect the perceived hue of transmission or reflection, or to select thespecific spectrum, or amount of energy, that is transmitted orreflected, including UV, visible, or IR light.

Numerous other combinations of thermotropic carrier (“host”) andorientation-dependent colorant (“guest”) materials are possible beyondthose discussed or enumerated here and may be employed without departingfrom the spirit of this embodiment.

FIG. 2 is a schematic, cross-section view of another exemplaryembodiment of a thermochromic filter device 200. As in the priorembodiment of FIG. 1, included ODC materials 201 are inside anorder-providing thermotropic carrier material 202. A polarizing film 203is placed between the incident light and the thermotropic carriermaterial 202 containing the included ODC materials 201. However,assuming that the ODC molecules interact more strongly with light alongtheir long axis, the order provided is now such that the includedmaterials 201 interact preferentially with one polarization of light.The polarizer 203 also interacts with this same polarization of light.Thus, in the lower temperature state, if together the “thermotropicpolarizer” created by the ordered state of the included materials 201and the polarizer 203 efficiently polarize the light, then approximately50% of the light is transmitted by the device. In the higher temperaturestate, the “thermotropic polarizer” created by the ordered state of theincluded materials 201 no longer exists. The polarizer 203 stillinteracts with one polarization of light, but now the included materialsinteract with both polarizations of light, reducing the amount of lighttransmitted to below 50%.

This arrangement may be advantageous for increasing the contrast ratioof a Guest-Host system, or for producing other desirable optical effects(e.g., particular combinations of absorption and reflection atparticular wavelengths) that would be difficult to achieve with theguest (ODC) and host (carrier) materials alone. The exact arrangement ofthe layer may deviate from the depiction in FIG. 2 without significantlyaffecting the functioning of the device. Optically speaking, it is oflittle consequence whether photons pass through the polarizer and thenthe guest-host system, or vice-versa. Various types of polarizers can beused, including absorptive, reflective, diffusive, and diffractivepolarizers. In addition, more than one polarizer may be employed, andvarious optional components such as substrates, adhesives, sealants,solubility promoters, bandblock filters, longpass filters, shortpassfilters, and fixed tints may be added in any combination withoutdeparting from the spirit of this embodiment.

However, it should be noted that if a retarder, waveblock, orbirefringence compensation film or layer is employed, then the orderingof the layers does matter. For example, the polarization axis of alinear polarizing film is typically parallel to the draw direction ofthe film. However, if light passes through the polarizer and then awaveblock layer, the resulting polarized light can be “rotated” suchthat its polarization axis occurs at 45 degrees (or some other desirableangle) to the draw direction. This may be useful in that in some cases a45-degree polarization axis allows for a simpler manufacturing process,as described in U.S. patent application Ser. No. 12/545,051 by Powerset. al. Alternatively, compensating to some angle slightly larger orsmaller than 45 degrees may help to “open up” the light transmission ofthe filter by effectively misaligning the polarizers, such that thecontrast ratio of the device is reduced and the blocking-state lighttransmission is increased, as described for example in U.S. PatentApplication #2009/0015902 to Powers et. al.

It may be desirable in some circumstances to place waveblocks on bothpolarizers in a two-polarizer device, or on all polarizers in amultiple-polarizer device. It may also be desirable in othercircumstances to place such optical films on only one polarizer. Forexample, two polarizers “rotated” by 45 degrees each may be comparableto one polarizer “rotated” by 90 degrees and one polarizer not rotatedat all. Reducing the number of waveblocks may reduce the cost of thefinal product while retaining the same functionality. Therefore, it maybe recognized that waveblocks, retarders, birefringence compensationfilms, birefringent materials of particular thickness, or other relatedpolarity-rotating materials or devices may be combined in a largevariety of ways in various implementations of this technology.

The amount of polarity rotation provided by a retarder/waveblock orbirefringence compensation film or coating is proportional to both thebirefringence and the thickness of the waveblock material. Thus, it isstraightforward to devise a film or coating to achieve very preciseamounts of polarity rotation, and the methods for doing so require nofurther elaboration here, except to note that achromatic waveplates willgenerally introduce fewer color anomalies than non-achromaticwaveplates. The implementation also encompasses versions where astandard polarizer and thermotropic polarizer have perpendicular orotherwise non-parallel polarization axes, negative dichroics withparallel alignment, with and without an ordinary (non-thermotropic)polarizer, and versions wherein the device becomes more reflective,absorptive, or fluorescent when hot.

FIG. 3. is a schematic, cross-section view of another exemplaryembodiment of a thermochromic filter device 300. As in the priorembodiments of FIGS. 1 and 2, included ODC materials 301 are inside anorder-providing, thermotropic carrier material 302. At a lowertemperature, a given percentage of the incoming light passes through theorder-providing material 302 as well as the included materials 301 dueto their ordered orientation with respect to the incoming light. At ahigher temperature, the order of the included materials is reduced (butthe order parameter is not zero), so that more of the incoming light isabsorbed or reflected due to the unordered orientation of the includedmaterials. Thus for this device, the reduction in transmitted light maybe more gradual than for the embodiment of FIG. 1. Note that this devicemay polarize light coming from directions other than the one indicatedin the figure at both the lower and higher temperatures, as the includedODC materials are in ordered orientations at both temperatures, and thusmay be considered a “thermotropic polarizer” for some purposes.

It should be understood that the structure and orientations depicted inFIG. 3 may exist as either the only possible states of the device, or asintermediate states. For example, a particular arrangement of ODCmaterials and thermotropic carrier materials may produce theorientations of FIG. 1 at extreme temperatures and the orientations ofFIG. 3 at more modest temperatures, without departing from the spirit ofeither embodiment or of this disclosure as a whole.

FIG. 4. is a schematic, cross-section view of an additional exemplaryembodiment of a thermochromic filter device 400. As in the priorembodiments of FIGS. 1, 2, and 3, included ODC materials 401 are insidean order-providing, thermotropic carrier material 402. However, at alower temperature, a given percentage of the incoming light passesthrough the order-providing material 402 as well as the included ODCmaterials 401 due to their ordered orientation with respect to theincoming light. Further, at a higher temperature, the order of theincluded ODC materials 401 is reduced (but the order parameter is notzero), so that more of the incoming light is absorbed or reflected dueto the unordered orientation of the included ODC materials 401. Thus forthis thermochromic filter device 400, the reduction in transmitted lightmay be more gradual than for the embodiment of FIG. 1. Again, thisthermochromatic filter device 400 polarizes light coming from directionsother than the one indicated in FIG. 4 at both the lower and highertemperatures. However, the director of the included ODC materials 401(determined by the system) is chosen in accordance with desirableinteractions of the thermochromatic filter device 400 with light thatvaries in incoming direction (e.g., such as with solar energy, whichvaries in incoming direction both due to rotation of the planet as wellas due to season).

The structure and orientations depicted in FIG. 4 may exist as eitherthe only possible states of the device, or as intermediate states. Forexample, a particular arrangement of ODC materials and thermotropiccarrier materials may produce the orientations of FIG. 1 at extremetemperatures and the orientations of FIG. 4 at more modest temperatures,without departing from the spirit of either embodiment or of the presentdisclosure as a whole.

The included ODC materials may be any number of materials includingdyes, rods, particles, or polymers in a thermotropic (e.g., nematic)liquid crystal carrier material. Properly selected ODC guest materialswill assume the order and director of the liquid crystal while theliquid crystal is in the nematic state (or other liquid crystallinestates such as smectic), and somewhat or completely lose their orderwhile the liquid crystal is in the isotropic state. Then if the liquidcrystal is in a liquid crystalline state (e.g., nematic) and alignedvertically between two transparent parallel surfaces, light travelingthrough the device perpendicular to the surfaces will not significantlyinteract with the included ODC material (e.g., positive dichroic dyes).However, as the temperature increases (i.e., above the isotropictemperature), the thermotropic liquid crystal will not have an alignedorder. Thus, the liquid crystal will be more randomly oriented and willnot impart order to the included materials, which will also be randomlyoriented and thus interact significantly more with light travelingthrough the device perpendicular to the surfaces. Note again here, theguest material need not be a liquid crystal.

In a further implementation of this embodiment, the included ODCmaterial may be an electrically conductive polymer. This selection isnot made for electrical reasons per se, but for the desirable opticalproperties (absorption and reflection) that are typical of electricallyconductive materials. Thus, the interactions with light may be selectedto be either reflective or absorptive, or any combination thereof. Inthe randomly oriented state, the reflections may not be specular, butrather diffusively reflective, which is desirable in many applications.

In some implementations of this embodiment, the included ODC materialsmay be inside a thermotropic carrier material (e.g., thermotropic liquidcrystal), which provides a director parallel to the surfaces (i.e., isaligned in parallel) and thus light traveling through the deviceperpendicular to the surfaces will interact with the included ODCmaterial (e.g., positive dichroic dyes) as a polarizer. One or morepolarizers that are part of the device may be oriented such that they donot interact with the light that is transmitted through the polarizerformed by the included materials. However, as the temperature increases(i.e., rises above isotropic temperature), the material (e.g., athermotropic liquid crystal) will not have an aligned order, but will bemore randomly oriented, and thus will not impart order to the includedmaterials. Thus, the included materials will also be randomly orientedand interact significantly more with light of the polarizationtransmitted by the polarizer(s), if any, and change how much light istransmitted.

In other implementations, the included ODC materials interact with lightsuch that when their director is perpendicular to the surfaces, theincluded materials interact with the light (e.g., absorb, reflect, orfluoresce the light) more strongly than when their director is parallelto the surfaces (i.e., negative dichroics).

While several exemplary embodiments are depicted and described herein,it should be understood that the present invention is not limited tothese particular configurations. For example, the polarizers (if any)employed in the structure may be linear or circular, absorptive orreflective, diffusive or specular, and/or fixed or thermotropic innature. One or more polarizers used in the device may be spectrallyselective or may be selected to have a high or low polarizingefficiency. The order-providing materials can be thermotropic liquidcrystals, ice/water, phase change materials, crystalline structures, orany of many forms of matter which can provide order to the included ODCmaterials. The polarizers, including thermotropic polarizers, may be inany relation to each other. The devices may be configured to become moretransmissive with increases in temperature. Negative and positivedichroic ODCs may also be combined.

In addition, it should be understood that in some cases the order anddirector may be provided by the ODC material itself (e.g., crystallinematerials), such that the “guest” and “host” functions are combined in asingle, carefully selected or constructed material. For example,molecular chains of polyacetylene can act as electrical “wires” and maybe an excellent candidate ODC “guest” material. However, polyacetylenechains also exhibit liquid crystal properties, and thus may beconsidered a “host” candidate as well, or a component of the host.

Alternatively or in addition, the included ODC “guest” materials and orthe thermotropic carrier or “host” materials may be attached to orconstrained by a polymer or polymer network that is part of thesubstrate material, or may be attached to one or more of the substrate'ssurfaces.

In another variant of the above embodiments, the order of the hostmaterial, and thus of the included ODC material, may also be changed byan electrical “override”. An electrical “override” may be present forthe order-providing material, for example by changing the order anddirector of a nematic liquid crystal through the use of torquingelectrical fields. Alternatively, the guest material may be the locus ofthe electrical “override” (e.g., as in a suspended particle device).This may be particularly effective in cases where the ODC “guest” orthermotropic “host” consist of, or include, an electrically conductivepolymer as described above.

The included materials may be selected to provide desired transmission,reflection, fluorescence, and absorption characteristics, spectrums,hues, or aesthetics, or to provide desirable energy transmission,absorption, and reflection characteristics. In addition, multiplethermochromic devices, of either the same type or of different types,may be combined to produce different aesthetic, optical, thermal,privacy, visual contrast, or solar heat gain properties. The amount oforder may locally or globally increase with temperature rather thandecrease, or the device may be constructed such that the transmission oflight increases with increasing temperature. The guest mixture may bemonochrome or black, tinted, fluorescent, and/or metameric.

In another possible implementation, the device may additionally be athermotropic polymer dispersed liquid crystal device. For this purpose,the Guest-Host system may be selected for low solubility in the polymer,or a low birefringence Host (e.g. liquid crystal) may be matched withthe optical index of the polymer to improve device performance andoptical clarity.

It should also be understood that any or all of the embodiments andvariants described above may be paired with a number of optionalcomponents without altering their essential nature or function. Thesemay include, but are not limited to, substrates, fixed tints, adhesives,sealants, wave plates, reflectors, partial reflectors, transreflectors,low-emissivity materials, UV-absorptive or reflective materials, and/orIR absorptive or reflective materials.

Additionally, there may be materials that provide more order at highertemperatures, or different amounts of order at different temperatures,such as the change in order and director with changes in temperaturesthat occurs in thermotropic liquid crystals that have both nematic andsmetic states. Devices thus may be based on changes in the director ororder with temperature rather than simply upon a loss of order withchanges in temperature. Additionally, the included ODC material may infact be simply in proximity to the order providing carrier materialrather than wholly dissolved or suspended within it, or may inducechanges in the amount of order the order-providing material provides atvarious temperatures.

Optional components such as coatings, films, spacers, fillers, orsupport structures may be added to suit the needs of a particularapplication or a particular manufacturing method, and degraded forms ofsome embodiments can be produced by deleting or substituting certaincomponents. The exact arrangement of the various layers can be differentthan is depicted here and, depending on the materials and wavelengthsselected, different layers can be combined as single layers, objects,devices, or materials, without altering the essential structure andfunction of the invention.

Although the description above contains many specificities, andreference to one or more individual embodiments, these should not beconstrued as limiting the scope of the invention but rather construed asmerely providing illustrations of certain exemplary embodiments of thisinvention. There are various possibilities for implementation ofdifferent materials and in different configurations and those skilled inthe art could make numerous alterations to the disclosed embodimentswithout departing from the spirit or scope of this invention.

In addition, although various embodiments of this invention have beendescribed above with a certain degree of particularity, all directionalreferences e.g., inside, proximal, distal, upper, lower, inner, outer,upward, downward, left, right, lateral, front, back, top, bottom, above,below, vertical, horizontal, clockwise, counterclockwise, left circular,and right circular are only used for identification purposes to aid thereader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Connection references, e.g., attached, coupled, connected,and joined are to be construed broadly and may include intermediatemembers between a collection of elements and relative movement betweenelements unless otherwise indicated. As such, connection references donot necessarily imply that two elements are directly connected and infixed relation to each other. Specific values cited in this text, suchas transition temperatures, clearing points, percentages of reflection,transmission or absorption are illustrative and shall not be limiting.More generally, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative only and not limiting. Changes in detail or structuremay be made without departing from the basic elements of the inventionas defined in the following claims.

1. A window comprising a thermochromic filter device incorporated into astructure of the window and further comprising an order-providing,thermotropic carrier material defining a director orientation; and anorientation-dependent colorant material included within the thermotropiccarrier material responsive in order to the director orientation;wherein the director orientation of the thermotropic carrier material isresponsive to temperature-induced changes in the thermotropic carriermaterial; the orientation-dependent colorant material changesorientation with the director orientation, whereby light transmissionproperties of the window vary with temperature as a result.